There is a system hang issue on imx6q which can easily be seen withrunning a cpu hotplug stress testing (hotplug secondary cores fromuser space via sysfs interface for thousands iterations).

It turns out that the issue is caused by coherency of the cpu thatis being shut down. When shutting down a cpu, we need to have thecpu exit coherency to prevent it from receiving cache, TLB, or BTBmaintenance operations broadcast by other CPUs in the cluster.